Question Performance of combining multiple textures in surface shader

Dear all,

I am a newbie in computer graphics and shader programming, here's my code for combining (concat, overlay) several 2d textures (they are all sprite sheets)

Code (CSharp):

1.             void surf(Input IN, inout SurfaceOutput o)
2.             {
3.                 fixed4 main = tex2D(_MainTex, IN.uv_MainTex) * _Color;
4.                 fixed4 outfit = tex2D(_OutFit, IN.uv_MainTex) * _Color;
5.                 fixed4 bag = tex2D(_Bag, IN.uv_MainTex) * _Color;
6.                 fixed4 head = tex2D(_Head, IN.uv_MainTex) * _Color;
7.                 fixed4 hand = tex2D(_Hand, IN.uv_MainTex) * _Color;
8.                 fixed4 back = tex2D(_Back, IN.uv_MainTex) * _Color;
9.  
10.                 fixed3 combine = lerp(main.rgb, outfit.rgb, outfit.a / 1);
11.                 fixed3 combine1 = lerp(combine.rgb, bag.rgb, bag.a / 1);
12.                 fixed3 combine2 = lerp(combine1.rgb, head.rgb, head.a / 1);
13.                 fixed3 combine3 = lerp(combine2.rgb, hand.rgb, hand.a / 1);
14.                 fixed3 combine4 = lerp(combine3.rgb, back.rgb, back.a / 1);
15.  
16.                 o.Albedo = combine4.rgb;
17.                 o.Alpha = main.a + outfit.a + bag.a + head.a + hand.a + back.a;
18.             }

Based on the code, there are six sheets to combine (same size, same format, with perfect alignment) with certain orders. Right now this shader did what I want perfectly, but I am seeking a more efficient way to combine them.

Previously I used several GameObjects, and each of them contains a sprite renderer to display different components. However, the old solution takes a lot of draw calls, especially after I enabled the sprite shadow.

The game targets the mobile platform, after changing to the shader, it reduced a lot. However, I believe that I can still somehow optimize the shader code.

Thanks for any suggestions. Cheers!

 

Not especially, no. That's about as optimal as you're going to get on a mobile device. Anything else you might try to do in the shader is just going to make it way, way more expensive. Even on desktop, there's not a ton more you can do.

The "better" option would be to combine all the layers by rendering them to a render texture, and use that pre-combined single texture instead.

 

Thank you bgolus! I will try your proposed solution.